Actuator

ABSTRACT

An actuator  100  of the type employing a two-degree-of-freedom vibration system includes: a pair of first mass portions  1, 11 ; a second mass portion  2  provided between the pair of first mass portions  1, 11 ; a pair of supporting portions  3, 3  for supporting the pair of first mass portions  1, 11  and the second mass portion  2 ; at least a pair of first elastic connecting portions  4, 4  which respectively connect the first mass portions  1, 11  to the supporting portions  3, 3  so that each of the first mass portions  1, 11  can rotate with respect to the supporting portions  3, 3 ; and at least a pair of second elastic connecting portions  5, 5  which respectively connect the second mass portion  2  to the first mass portions  1, 11  so that the second mass portion  2  can rotate with respect to the first mass portions  1, 11 . Each of the first mass portions  1, 11  is driven by the application of an alternating voltage, causing the second mass portion  2  to rotate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional patent application of U.S. Ser. No.10/976,247 filed Oct. 27, 2004, claiming priority to JP 2003-369545filed Oct. 29, 2003, all of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an actuator, and in particular relatesto an actuator of the type employing a two-degree-of-freedom vibrationsystem.

2. Description of the Prior Art

There is known a polygon mirror (rotary polyhedron) as an actuatorprovided in laser printers, for example. In such a printer, in order toachieve higher-resolution and higher-quality printed output as well ashigher-speed printing, it is necessary to rotate the polygon mirror athigher speed. Currently, an air bearing is used to rotate the polygonmirror at high speed with stability. However, there is a problem in thatit is difficult to rotate the polygon mirror at much higher speed thanthe speed available at the present. Further, although a larger motor isrequired in order to rotate the polygon mirror at higher speed, use ofsuch a larger motor arises a problem in that it is difficult tominiaturize the size of an apparatus in which the polygon mirror isused. Furthermore, use of such a polygon mirror arises another problemin that the structure of the apparatus becomes necessarily complicated,thus leading to increased manufacturing cost.

On the other hand, a single-degree-of-freedom torsional vibrator asshown in FIG. 10 has been proposed since the early stages of research inthe field of actuators. Since this vibrator uses flat electrodes whichare arranged in parallel with each other, it can have quite simplestructure (see K. E. Petersen: “Silicon Torsional Scanning Mirror”,IBMJ. Res. Develop., Vol. 24 (1980), P. 631, for example). Further, asingle-degree-of-freedom electrostatic drive type vibrator obtained bymodifying the torsional vibrator described above so as to have acantilever structure has also been proposed (see Kawamura et al.:“Research in micromechanics using Si”, Proceedings of the Japan Societyfor Precision Engineering Autumn Conference (1986), P. 753, forexample).

FIG. 10 shows such a single-degree-of-freedom electrostatic drive typetorsional vibrator. In the torsional vibrator in FIG. 10, a movableelectrode plate 300 made of monocrystalline silicon is fixed at endfixing portions 300 a thereof to the both ends of a glass substrate 1000through spacers 200. The movable electrode plate 300 includes a movableelectrode portion 300 c which is supported by the end fixing portions300 a through narrow torsion bars 300 b. Further, a fixed electrode 400is provided on the glass substrate 1000 so as to be opposed to themovable electrode portion 300 c through a predetermined electrodeinterval. Specifically, the fixed electrode 400 is arranged in parallelwith the movable electrode portion 300 c through the electrode intervaltherebetween. The fixed electrode 400 is connected to the movableelectrode plate 300 via a switch 600 and a power source 500.

In the torsional vibrator having the structure described above, when avoltage is applied across the movable electrode portion 300 c and thefixed electrode 400, the movable electrode portion 300 c rotates aroundthe axis of the torsion bars 300 b due to electrostatic attraction.Since electrostatic attraction is inversely proportional to the squareof an electrode interval, it is preferable for this type ofelectrostatic actuator to have a small electrode interval between themovable electrode portion 300 c and the fixed electrode 400. However, insuch a single-degree-of-freedom torsional vibrator described above, themovable electrode portion 300 c which serves as a movable portion isalso provided with the electrode. Therefore, if the electrode intervalbecomes too small, a movable range (rotation angle) of the movableelectrode portion 300 c is necessarily limited. On the other hand, inorder to enlarge the movable range of the movable electrode portion 300c, it is necessary to widen the electrode interval and this in turnneeds a large driving voltage. Namely, such a single-degree-of-freedomtorsional vibrator described above involves a problem in that it isdifficult to achieve both of low-voltage driving and large displacement.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide anactuator capable of operating at low voltage and achieving a largedisplacement (that is, large rotation angle or large deflection angle).

In order to achieve the object, the present invention is directed to anactuator of the type employing a two-degree-of-freedom vibration system.The actuator of the present invention includes:

a pair of first mass portions;

a second mass portion provided between the pair of first mass portions;

a pair of supporting portions for supporting the pair of first massportions and the second mass portion;

at least a pair of first elastic connecting portions which respectivelyconnect the first mass portions to the supporting portions so that eachof the first mass portions can rotate with respect to the supportingportions; and

at least a pair of second elastic connecting portions which respectivelyconnect the second mass portion to the first mass portions so that thesecond mass portion can rotate with respect to the first mass portions;

wherein each of the first mass portions is driven by the application ofan alternating voltage, causing the second mass portion to rotate.

According to the present invention described above, it is possible toprovide an actuator capable of operating at low voltage and achieving alarge rotation angle (that is, large deflection angle).

In the actuator according to the present invention, it is preferredthat, in the case where a length between a central axis for the rotationof one of the first mass portions and an end portion of the one of thefirst mass portions in a direction substantially perpendicular to thecentral axis for the rotation is defined as L1, a length between acentral axis for the rotation of the other of the first mass portionsand an end portion of the other of the first mass portions in adirection substantially perpendicular to the central axis for therotation is defined as L2, and a length between a central axis for therotation of the second mass portion and an end portion of the secondmass portion in a direction substantially perpendicular to the centralaxis for the rotation is defined as L3, then L1 and L3 satisfy therelations: L1<L3 and L2<L3.

This makes it possible to provide an actuator capable of operating atlow voltage and achieving a large rotation angle (that is, largedeflection angle) more easily and reliably.

In the actuator according to the present invention, it is preferred thatthe length L1 is substantially the same as the length L2.

This makes it possible to control the actuator easily, and therefore itis possible to provide an actuator capable of operating at low voltageand achieving a large rotation angle (that is, large deflection angle)more easily and reliably.

In the actuator according to the present invention, it is preferred thatthe frequency of the alternating voltage is set so as to besubstantially the same as a lower resonance frequency of resonancefrequencies of the two-degree-of-freedom vibration system at which thepair of first mass portions and the second mass portion resonate.

This makes it possible to provide an actuator capable of operating atlow voltage and achieving a large rotation angle (that is, largedeflection angle) . Further, it is also possible to increase a rotationangle (deflection angle) of the second mass portion while vibration(amplitude) of the first mass portion is suppressed.

In the actuator according to the present invention, it is preferred thatthe actuator includes:

a counter substrate provided so as to be opposed to the pair ofsupporting portions through a predetermined distance, the countersubstrate having a surface facing the supporting portions;

at least a pair of electrodes provided on the surface of the countersubstrate at a position corresponding to the position of the one of thefirst mass portions; and

at least a pair of electrodes provided on the surface of the countersubstrate at a position corresponding to the position of the other ofthe first mass portions;

wherein each of the first mass portions is driven by electrostatic forcegenerated between each of the first mass portions and the correspondingelectrodes.

This makes it possible to further increase a rotation angle (deflectionangle) of the second mass portion.

In the actuator according to the present invention, it is also preferredthat the counter substrate includes an opening at a positioncorresponding to the position of the second mass portion.

Such an actuator makes it possible to prevent a contact between thesecond mass portion and the counter substrate when the second massportion rotates, and as a result, it is possible to further increase arotation angle (deflection angle) of the second mass portion.

In the actuator according to the present invention, it is also preferredthat the second mass portion includes a light reflection portion.

Such an actuator makes it possible to change optical (light) path easilywhen it is used in an optical scanner, for example.

In the actuator according to the present invention, it is also preferredthat, in the case where the spring constant of the first elasticconnecting portion is defied as k₁ and the spring constant of the secondelastic connecting portion is defined as k₂, k₁ and k₂ satisfy therelation: k₁>k₂.

This makes it possible to further increase rotation angle (deflectionangle) of the second mass portion while vibration (amplitude) of thefirst mass portion is suppressed.

In the actuator according to the present invention, it is also preferredthat, in the case where the moment of inertia of the pair of first massportions is defined as J₁ and the moment of inertia of the second massportion is defined as J₂, J₁ and J₂ satisfy the relation: J₁≦J₂.

This makes it possible to further increase the rotation angle(deflection angle) of the second mass portion while the vibration(amplitude) of the first mass portion is suppressed.

In the actuator according to the present invention, it is also preferredthat at least one of the pair of first elastic connecting portions andthe pair of second elastic connecting portions includes a piezoresistiveelement.

This makes it possible to detect rotation angles and rotationfrequencies, for example. Further, it is also possible to utilize thedetection results to control the attitude of the second mass portion.

The above and other objects, features and advantages of the presentinvention will readily become more apparent when the following detaileddescription of the preferred embodiments of the present invention willbe considered taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view which shows a first embodiment of the actuatoraccording to the present invention.

FIG. 2 is a cross-sectional view which shows the first embodiment of theactuator according to the present invention.

FIG. 3 is a plan view which shows a counter substrate and electrodes ofthe first embodiment.

FIG. 4 is a drawing which shows an example of the alternating voltage tobe applied to the actuator shown in FIG. 1.

FIG. 5 is a graph which shows the frequency of an alternating voltageapplied and the resonance curves of a first mass portion and a secondmass portion.

FIG. 6 is a step diagram which shows one example of a method formanufacturing the actuator according to the present invention.

FIG. 7 is a plan view which shows a second embodiment of the actuatoraccording to the present invention.

FIG. 8 is a plan view which shows a third embodiment of the actuatoraccording to the present invention.

FIG. 9 is a plan view which shows a fourth embodiment of the actuatoraccording to the present invention.

FIG. 10 is a perspective view which shows a conventional actuator.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of an actuator according to thepresent invention will be described with reference to the appendeddrawings.

First Embodiment

First, a first embodiment of the actuator according to the presentinvention will be described. FIG. 1 is a plan view which shows the firstembodiment of the actuator according to the present invention. FIG. 2 isa cross-sectional view which shows the first embodiment of the actuatoraccording to the present invention. FIG. 3 is a plan view which shows acounter substrate and electrodes of the first embodiment. FIG. 4 is adrawing which shows an example of the alternating voltage to be appliedto the actuator shown in FIG. 1. FIG. 5 is a graph which shows thefrequency of an alternating voltage applied and the resonance curves ofa first mass portion and a second mass portion. In the followingdescription, it is to be noted that the upper side, the lower side, theright side and the left side in FIGS. 1 and 3 will be referred to as the“upper side”, “lower side”, “right side” and the “left side”,respectively.

An actuator 100 shown in FIG. 1 includes a first mass portion (that is,a driving portion) 1, a second mass portion (that is, a movable portion)2, and a pair of supporting portions 3. In the actuator 100, the secondmass portion 2 is positioned at the center thereof, and the first massportions 1, 11 are provided at one end side (right side in FIG. 1) andthe other side (left side in FIG. 1) of the second mass portion 2,respectively. Further, one supporting portion 3 is arranged at the rightside of the first mass portion 1 in FIG. 1, while the other supportingportion 3 is arranged at the left side of the first mass portion 11 inFIG. 1.

In the present embodiment, as shown in FIG. 1, the first mass portions1, 11 has substantially the same shape and size, and are symmetricallyprovided with respect to the second mass portion 2. Each of the firstmass portions 1 and 11, the second mass portion 2, and the supportingportions 3, 3 is made of silicon or the like, for example. On thesurface of the second mass portion 2 of this embodiment (that is, thesurface of the second mass portion 2 which does not face a countersubstrate 6 which will be described later), there is provided a lightreflection portion 21.

Further, as shown in FIG. 1, the actuator 100 includes a pair of firstelastic connecting portions 4, 4 and a pair of second elastic connectingportions 5, 5. The pair of first elastic connecting portions 4, 4connect the first mass portions 1, 11 to the supporting portions 3, 3,respectively, so that each of the first mass portions 1, 11 can rotatewith respect to the corresponding supporting portion 3. The pair ofsecond elastic connecting portions 5, 5 connect the second mass portion2 to the first mass portions 1, 11, respectively, so that the secondmass portion 2 can rotate with respect to the first mass portions 1, 11.In other words, the second mass portion 2 is connected to the first massportions 1, 11 via the second elastic connecting portions 5, 5,respectively, and the first mass portions 1, 11 are connected to thesupporting portions 3, 3 via the first elastic connecting portions 4, 4,respectively. In this case, the first elastic connecting portions 4, 4and the second elastic connecting portions 5, 5 are coaxially providedto constitute a central axis for the rotation of the first and secondmass portions 1, 11, 2 (that is, rotational axis) 41.

As shown in FIG. 2, the supporting portions 3, 3 are joined to spacers 9through insulating portions 8, 8, respectively. Each of the insulatingportions 8 is made of oxides or nitrides of silicon, for example, andeach of the spacers 9 is made of silicon, for example. Further, as shownin FIG. 2, the actuator 100 of this embodiment includes the countersubstrate 6. The counter substrate 6 is provided so as to be opposed tothe supporting portions 3, 3 through a predetermined distance. Thecounter substrate 6 is made of various glass materials or silicon, forexample.

As shown in FIG. 2, the supporting portions 3, 3 are respectivelysupported on the counter substrate 6 through the spacers 9, 9 and theinsulating portions 8, 8. As shown in FIGS. 2 and 3, the countersubstrate 6 has an opening 61 at a position corresponding to theposition of the second mass portion 2. Further, on the counter substrate6, there are provided two pairs of electrodes 7 at a positioncorresponding to the position of the first mass portions 1, 11,respectively. The two pairs of electrodes 7 are provided so as to becomesubstantially symmetrical to each other in each pair of electrodes 7with respect to the surface including the central axis for rotation 41(that is, the rotational axis of the first mass portions 1, 11) andperpendicular to the counter substrate 6.

The two pair of electrodes 7 are connected to the first mass portions 1,11 via a power source (not shown in the drawings) so that an alternatingvoltage (driving voltage) can be applied across the first mass portions1, 11 and the two pair of electrodes 7, respectively. In this regard,insulating films (not shown in the drawings) are respectively providedon the surfaces of the first mass portions 1, 11 (that is, the surfacesof the first mass portions 1, 11 facing the electrodes 7) to prevent ashort circuit. In such a two-degree-of-freedom vibration type actuatorhaving the structure as described above, the first mass portions 1, 11and the first elastic connecting portions 4, 4 constitute a firstvibration system, and the second mass portion 2 and the second elasticconnecting portions 5, 5 constitute a second vibration system.

A sinusoidal wave (alternating voltage) or the like is applied acrosseach of the first mass portions 1, 11 and the corresponding electrodes7, for example. Specifically, for example, when the first mass portions1, 11 are connected to ground, and voltage signals each having awaveform as shown in FIGS. 4A and 4B are respectively applied to the twoelectrodes 7, 7 at the upper side in FIG. 3 and the two electrodes 7, 7at the lower side in FIG. 3, electrostatic force is generated betweenthe first mass portions 1, 11 and the corresponding electrodes 7. Theforce attracting the first mass portions 1, 11 toward the electrodes 7due to the generated electrostatic force changes depending on the phaseof each of the waveforms so that the first mass portions 1, 11 rotatearound the central axis for rotation 41 (the axis of the first elasticconnecting portions 4, 4) (that is, the first mass portions 1,11 vibrateby the application of the alternating voltage). The vibration of each ofthe first mass portions 1, 11 causes the second mass portion 2, which isconnected to both of the first mass portions 1, 11 through the secondelastic connecting portions 5, 5, to rotate around the central axis forrotation 41 (the axis of the second elastic connecting portions 5, 5)(that is, the second mass portion 2 also vibrates or is deflected).

Here, a length (distance) between the central axis for rotation 41 onthe first mass portion 1 and an end portion of the first mass portion 1in a direction substantially perpendicular to the central axis forrotation 41 is defined as L1, a length (distance) between the centralaxis for rotation 41 on the first mass portion 11 and an end portion ofthe first mass portion 11 in a direction substantially perpendicular tothe central axis for rotation 41 is defined as L2, and a length(distance) between the central axis for rotation on the second massportion 2 and an end portion of the second mass portion 2 in a directionsubstantially perpendicular to the central axis for rotation 41 isdefined as L3. Since the first mass portions 1, 11 are providedindependently of each other, the first mass portions 1, 11 do notinterfere in the second mass portion 2. Thus, it is possible to make thelengths L1 and L2 smaller regardless of the size of the second massportion 2. This makes it possible to enlarge the rotation angle of eachof the first mass portions 1, 11 (that is, deflection angle of thesecond mass portion 2 with respect to the direction parallel to thesurface on which the electrodes 7 of the counter substrate 6 areprovided), and therefore it is possible to enlarge the rotation angle ofthe second mass portion 2.

Further, by making the lengths L1 and L2 smaller, it is possible to makethe distance between the respective first mass portions 1, 11 and eachof the corresponding electrodes 7 smaller. This makes it possible toenlarge the electrostatic force, and therefore it is possible todiminish the alternating voltage applied between each of the first massportions 1, 11 and each of the electrodes 7. In this regard, it ispreferable that the lengths L1, L2 and L3 (that is, sizes of the firstmass portions 1, 11 and the second mass portion 2) are set so as tosatisfy the relations: L1<L3 and L2<L3.

By satisfying the relations described above, it is possible to make thelengths L1, L2 further smaller. This makes it possible to enlarge therotation angles of the first mass portions 1, 11, and therefore it ispossible to further enlarge the deflection angle of the second massportion 2. In this case, it is preferable that the maximum deflectionangle of the second mass portion 2 is set so as to become 20° or more.

Moreover, by making the lengths L1, L2 smaller, it is possible tofurther reduce the distance between each of the first mass portions 1,11 and each of the corresponding electrodes 7, and therefore it ispossible to further diminish the alternating voltage applied betweeneach of the first mass portions 1, 11 and each of the correspondingelectrodes 7. Therefore, it is possible to realize (achieve) thelow-voltage driving for the first mass portions 1, 11 and the largedisplacement of the second mass portion 2. For example, in the casewhere the actuator described above is applied to an optical scanner usedin apparatuses such as laser printer, confocal scanning lasermicroscope, it is possible to make the apparatus smaller more easily.

In this regard, as mentioned above, although the lengths L1 and L2 areset so as to have substantially the same size in this embodiment, it isno wonder that the length L1 may be different from the length L2. Itshould be noted that such a two-degree-of-freedom vibration typeactuator has a frequency characteristic as shown in FIG. 5 between theamplitudes (vibrations) of the first mass portions 1, 11 and the secondmass portion 2 and the frequency of the applied alternating voltage.

Namely, the two-degree-of-freedom vibration system constituted from thefirst mass portions 1, 11, the first elastic connecting portions 4, 4,the second mass portion 2 and the second elastic connecting portions 5,5 has two resonance frequencies fm₁ (kHz) and fm₃ (kHz) (where, fm₁<fm₃)at which the amplitudes of the first mass portions 1, 11 and the secondmass portion 2 become large, and one antiresonance frequency fm₂ (kHz)at which the amplitude of the first mass portions 1, 11 becomessubstantially zero.

In this actuator 100, it is preferable that the frequency F of analternating voltage to be applied across each of the first mass portions1, 11 and the electrodes 7 is set so as to be substantially the same asa lower resonance frequency of the two resonance frequencies, that is,the frequency F is set so as to be substantially the same as fm₁. Bysetting the frequency F (kHz) of an alternating voltage to be applied soas to be substantially the same as fm₁ (kHz), it is possible to increasethe rotation angle (deflection angle) of the second mass portion 2 whilethe vibration of the first mass portions 1, 11 is suppressed. In thisregard, it is to be noted that, in this specification, the fact that F(kHz) is substantially the same as fm₁ (kHz) means that F and fm₁satisfy the relation: (fm₁−1)≦F≦(fm₁+1).

The average thickness of each of the first mass portion 1, 11 ispreferably in the range of 1 to 1,500 μm, more preferably it is in therange of 10 to 300 μm. Similarly, the average thickness of the secondmass portion 2 is preferably in the range of 1 to 1,500 μm, morepreferably it is in the range of 10 to 300 μm.

The spring constant of each of the first elastic connecting portions 4,4 (k₁) is preferably in the range of 1×10⁻⁴ to 1×10⁴ Nm/rad, morepreferably it is in the range of 1×10⁻² to 1×10³ Nm/rad, further morepreferably it is in the range of 1×10⁻¹ to 1×10² Nm/rad. By setting thespring constant of each of the first elastic connecting portions 4, 4(k₁) to a value within the above range, it is possible to furtherincrease the rotation angle (deflection angle) of the second massportion 2.

Similarly, the spring constant of each of the second elastic connectingportions 5, 5 (k₂) is preferably in the range of 1×10⁻⁴ to 1×10⁴ Nm/rad,more preferably it is in the range of 1×10⁻² to 1×10³ Nm/rad, furthermore preferably it is in the range of 1×10⁻¹ to 1×10² Nm/rad. By settingthe spring constant of each of the second elastic connecting portions 5,5 (k₂) to a value within the above range, it is possible to furtherincrease the rotation angle (deflection angle) of the second massportion 2 while the vibration of each of the first mass portions 1, 11is suppressed.

In the case where the spring constant of each of the first elasticconnecting portions 4, 4 is defined as k₁, and the spring constant ofeach of the second elastic connecting portions 5, 5 is defined as k₂, itis preferred that k₁ and k₂ satisfy the relation: k₁>k₂. This makes itpossible to further increase the rotation angle (deflection angle) ofthe second mass portion 2 while the vibration of each of the first massportions 1, 11 is suppressed.

Further, in the case where the moment of inertia of each of first massportions 1, 11 is defined as J₁ and the moment of inertia of the secondmass portion 2 is defined as J₂, it is preferred that J₁ and J₂ satisfythe relation: J₁≦J₂, and more preferably they satisfy the relation:J₁<J₂. This makes it possible to further increase the rotation angle(deflection angle) of the second mass portion 2 while the vibration ofeach of the first mass portions 1, 11 is suppressed.

Now, the natural frequency of the first vibration system ω₁ can bedetermined by the formula: ω₁=(k₁/J₁)^(1/2) in the case where J₁represents the moment of inertia of each of the first mass portions 1,11 and k₁ represents the spring constant of each of the first elasticconnecting portions 4, 4. The natural frequency of the second vibrationsystem ω₂ can be determined by the formula: ω₂=(k₂/J₂)^(1/2) in the casewhere J₂ represents the moment of inertia of the second mass portion 2,and k₂ represents the spring constant of each of the second elasticconnecting portions 5, 5.

It is preferable that the natural frequency of the first vibrationsystem ω₁ and the natural frequency of the second vibration system ω₂determined in such a manner described above satisfy the relation: ω₁>ω₂.This makes it possible to further increase the rotation angle(deflection angle) of the second mass portion 2 while the vibration ofeach of the first mass portions 1, 11 is suppressed.

In this regard, in the actuator 100 of this embodiment, it is preferredthat the actuator 100 has a piezoresistive element in at least one ofthe pair of first elastic connecting portions 4, 4 and the pair ofsecond elastic connecting portions 5, 5 thereof. This makes it possibleto detect rotation angles and rotation frequencies, for example.Further, it is also possible to utilize the detection results to controlthe attitude of the second mass portion 2.

Next, one example of a method of manufacturing the actuator 100 as shownin FIGS. 1 and 2 will be described with reference to the accompanyingdrawings. FIG. 6 is a step diagram which shows one example of a methodof manufacturing the actuator 100. In this example, the actuator 100 ismanufactured through the following three steps.

<First Step>

First, as shown in FIG. 6A, an SOI substrate 50 constituted from a firstSi layer 40, an SiO₂ layer 8′, and a second Si layer 9′ is prepared.Next, as shown in FIG. 6B, the first Si layer 40 is subjected to etchingto form the first mass portions 1, 11, the second mass portion 2, thesupporting portions 3, 3, the first elastic connecting portions 4, 4 andthe second elastic connecting portions 5, 5. Next, as shown in FIG. 6C,the second Si layer 9′ is subjected to etching to form the spacers 9, 9.Then, as shown in FIG. 6D, the light reflection portion 21 is formed onthe second mass portion 2 by a vacuum evaporation method or the like toobtain an upper substrate 60.

<Second Step>

First, as shown in FIG. 6E, a glass substrate 6′ is prepared. Next, asshown in FIG. 6F, the glass substrate 6′ is subjected to etching to formthe counter substrate 6 having the opening 61. Then, as shown in FIG.6G, the electrodes 7 are formed on the counter substrate 6 by a vacuumevaporation method or the like to obtain a lower substrate 70.

<Third Step>

As shown in FIG. 6H, the upper substrate 60 obtained in the first stepand the lower substrate 70 obtained in the second step are bonded byanode bonding, for example. Next, as shown in FIG. 6I, a part of theSiO₂ layer 8′, which is a part other than a part sandwiched between thesupporting portions 3, 3 and the spacers 9, 9, is removed by etching toform the insulating portions 8, 8. In this way, the actuator 100 ismanufactured. In this regard, it is to be noted that the second step maybe carried out concurrently with the first step, or may be carried outprior to the first step.

Second Embodiment

Next, a second embodiment of the actuator according to the presentinvention will be described. FIG. 7 is a plan view which shows thesecond embodiment of the actuator according to the present invention.Hereinafter, an actuator 100A shown in FIG. 7 will be described byfocusing on the difference between the first and second embodiments, andtherefore a description of the same points will be omitted.

As shown in FIG. 7, the actuator 100A of this embodiment includes twopairs of first elastic connecting portions 4′ and two pairs of secondelastic connecting portions 5′. The two pairs of first elasticconnecting portions 4′ connect the first mass portions 1, 11 to thesupporting portions 3, 3, respectively, so that each of the first massportions 1, 11 can rotate with respect to the corresponding supportingportion 3. The two pairs of second elastic connecting portions 5′connect the second mass portion 2 to the first mass portions 1, 11,respectively, so that the second mass portion 2 can rotate with respectto the first mass portions 1, 11.

With such a structure, it is possible to control the rotation angle(deflection angle) of the second mass portion 2 more reliably. It shouldbe noted that, in such a case, that is, in the case where the actuator100A includes the two pairs of first elastic connecting portions 4′ andthe two pairs of second elastic connecting portions 5′ as thisembodiment, the spring constants k₁ and k₂ thereof is determined on theassumption that the two elastic connecting portions 4′ connected betweenone of the supporting portions 3 and one of the first mass portions 1,11 are equivalent to the single elastic connecting portion 4 of thefirst embodiment which is disposed at substantially the same position asthe two elastic connecting portions 4′ of this second embodiment.

Third Embodiment

Next, a third embodiment of the actuator according to the presentinvention will be described. FIG. 8 is a plan view which shows the thirdembodiment of the actuator according to the present invention.Hereinafter, an actuator 100B shown in FIG. 8 will be described byfocusing on the difference between the first and third embodiments, andtherefore a description of the same points will be omitted. The actuator100B of this embodiment is driven by electromagnetic force (that is, byLorentz force).

Specifically, as shown in FIG. 8, the actuator 100B includes fourterminals 10 provided in the supporting portions 3, 3 through insulatingfilms (not shown in FIG. 8), two coils 20 respectively provided on thesurfaces of the first mass portions 1, 11 (that is, the surfaces of thefirst mass portions 1, 11 which do not face the counter substrate 6), apair of permanent magnets 30, 30 provided on both sides of the firstmass portions 1, 11 so that the first mass portions 1, 11 are placedtherebetween.

The pair of permanent magnets 30, 30 are arranged so that the south poleof one magnet 30 and the north pole of the other magnet 30 are opposedto each other. The end portions of each of the two coils 20, 20 areconnected to the corresponding two terminals 10, 10, respectively.Further, each of the terminals 10 is connected to a power source (notshown in the drawings) so that an alternating voltage can be applied toeach of the coils 20, 20. In this embodiment, when an alternatingvoltage is applied to each of the coils 20, 20, Lorentz force isgenerated between each of the coils 20 (first mass portions 1, 11) andthe permanent magnets 30, and the generated Lorentz force drives theactuator 100B.

Fourth Embodiment

Next, a fourth embodiment of the actuator according to the presentinvention will be described. FIG. 9 is a plan view which shows thefourth embodiment of the actuator according to the present invention.Hereinafter, an actuator 100C shown in FIG. 9 will be described byfocusing on the difference between the first and fourth embodiments, andtherefore a description of the same points will be omitted. The actuator100C of this embodiment is driven by two piezoelectric actuators (thatis, two actuators each having a piezoelectric element) 31, 31respectively provided on the surfaces of the first mass portions 1, 11(that is, the surface opposite to the surface on which the countersubstrate 6 is provided).

Specifically, as shown in FIG. 9, the actuator 100C includes a pair ofpiezoelectric actuators 31, 31 provided at one end portion (a part) ofthe surface of each of the first mass portions 1, 11. In the actuator100C of this embodiment, distortion (expansion and contraction) isgenerated on the first mass portions 1, 11 by the driving of thepiezoelectric actuators 31, 31 to drive the second mass portion 2.

In this embodiment, by providing the piezoelectric actuators 31, 31 onthe first mass portions 1, 11, respectively, it is no need to providethe electrodes (driving electrodes) 7, and therefore it is possible toreduce the manufacturing costs thereof. Further, since the drivingelectrodes 7 are not required, it is possible to arrange the opening 61on the positions corresponding to the first mass portions 1, 11. Thismakes it possible to enlarge the rotation angle of each of the firstmass portions 1, 11.

Further, in this embodiment, one (or one-layer) piezoelectric actuator31 is provided on each of the first mass portions 1, 11, but the presentinvention is not limited to this structure. For example, two or more (ortwo-or-more-layer) piezoelectric actuator such as a bimorph typepiezoelectric actuator may be provided. The bimorph type piezoelectricactuator is an actuator having two-layer structure piezoelectricactuator (that is, two piezoelectric actuators) that can generateflexural oscillation in which one of the two piezoelectric actuators issubjected to vibration in a compressed direction thereof at the sametime when the other is subjected to vibration in an expanded directionthereof.

In this regard, in this embodiment, the piezoelectric actuators 31, 31are respectively provided at the end portions of the surfaces of thefirst mass portions 1, 11, but the present invention is not limited tothis structure. For example, the piezoelectric actuator 31 may beprovided at the whole area of the surface of each of the first massportions 1, 11. Alternatively, the piezoelectric actuator 31 may beprovided at the end portion or the whole area of the surface of each ofthe first mass portions 1, 11 which faces the counter substrate 6.

The actuators described above based on the first to fourth embodimentscan be preferably applied to optical scanners to be used in laserprinters, bar-code readers, confocal scanning laser microscopes and thelike, or displays for imaging, for example.

Although the actuator according to the present invention has beendescried with reference to the embodiments shown in the drawings, thepresent invention is not limited thereto. For example, so long as thesame or similar functions are achieved, it is possible to make variouschanges and additions to each portion of the actuator of the presentinvention. Further, each of the actuators of the embodiments describedabove has the pair or two pairs of first elastic connecting portions 4or 4′, but the actuator according to the present invention is notlimited thereto and may have three or more pairs of first elasticconnecting portions 4, for example.

Similarly, each of the actuators of the embodiments described above hasthe pair or two pairs of second elastic connecting portions 5 or 5′, butthe actuator according to the present invention is not limited theretoand may have three or more pairs of second elastic connecting portions 5or 5′, for example.

Moreover, in each of the actuators of the embodiments described above,the light reflection portion 21 is provided on the surface of the secondmass portion 2 which does not face the counter substrate 6, but in theactuator according to the present invention, the light reflectionportion 21 may be provided on the opposite surface of the second massportion 2, or may be provided on both surfaces of the second massportion 2, for example.

Furthermore, in each of the actuators of the first and secondembodiments described above, the electrodes 7 are provided on thecounter substrate 6, but in the actuator according to the presentinvention, the electrodes 7 may be provided on the first mass portion 1,or may be provided on both of the counter substrate 6 and the first massportion 1, respectively. Moreover, in each of the actuators of the firstand second embodiments described above, the two pairs of electrodes 7are respectively provided at the positions corresponding to the firstmass portions 1, 11, but the actuator according to the present inventionis not limited thereto. For example, one or three or more electrode 7may be provided at each of the corresponding positions.

In this regard, in the case where one electrode 7 is provided at each ofthe positions corresponding to the first mass portions 1, 11, it ispreferable that sinusoidal wave (alternating voltage) to which an offsetvoltage is added and in which the minimum electric potential becomesground potential is applied to the one electrode 7, for example.

Further, in each of the actuators of the embodiments described above,the first elastic connecting portions 4 or 4′ and the second elasticconnecting portions 5 or 5′ have shapes shown in the drawings, but inthe actuator according to the present invention, the shapes thereof arenot limited thereto and they may have a crank shape or a branched shape,for example.

Moreover, in each of the actuators of the first and second embodimentsdescribed above, the insulating film is provided on the surface of eachof the first mass portions 1, 11, which is a surface facing theelectrodes 7, for preventing a short circuit, but in the actuatoraccording to the present invention, the insulating film may be providedon the surface of the electrodes 7 or may be provided on the surfaces ofboth of the first mass portions 1, 11 and the electrodes 7, for example.

Furthermore, in the actuator of the third embodiment described above,the coil 20 is provided on the surface of each of the first massportions 1, 11 which does not face the counter substrate 6, but in theactuator according to the present invention, the coil 20 may be providedon the opposite surface of each of the first mass portions 1, 11, or maybe provided inside each of the first mass portions 1, 11, for example.

Further, in the example of the manufacturing method of the actuatordescribed above, the upper substrate 60 is integrally formed, but theupper substrate 60 is not limited to one integrally formed. For example,a substrate obtained by integrally forming the first mass portions 1,11, the second mass portion 2, the supporting portions 3, 3, the firstelastic connecting portions 4, 4 and the second elastic connectingportions 5, 5 may be bonded to the lower substrate 70 through spacers 9,9 formed of glass or the like. Alternatively, each of these portions maybe separately formed, and then the thus obtained portions may beassembled by bonding.

1. An actuator of the type employing a two-degree-of-freedom vibrationsystem, the actuator comprising: a pair of first mass portions; a secondmass portion provided between the pair of first mass portions; a pair ofsupporting portions for supporting the pair of first mass portions andthe second mass portion; a pair of first elastic connecting portionswhich respectively connect the first mass portions to the supportingportions so that each of the first mass portions can rotate with respectto the supporting portions, wherein each of the first connectingportions comprises a pair of elastic connecting members which arearranged so as to have a substantially V-shape form; and a pair ofsecond elastic connecting portions which connect the second mass portionto the respective first mass portions so that the second mass portioncan rotate with respect to the first mass portions, wherein each of thesecond elastic connecting portions comprises a pair of elasticconnecting members which arranged so as to have a substantially V-shapeform; wherein each of the first mass portions is driven by theapplication of an alternating voltage, causing the second mass portionto rotate.
 2. The actuator as claimed in claim 1, wherein each of thepair of first elastic connecting portions and the pair of second elasticconnecting portions each having the V-shape form has an apex and twobase ends, in which a central axis for rotation of the first massportions and the second mass portion extends through the apexes of thefirst and second elastic connecting portions.
 3. The actuator as claimedin claim 2, wherein each of the first connecting portions each havingthe V-shape form is connected to the corresponding supporting portion atits apex and connected to the corresponding first mass portion at itsbase ends.
 4. The actuator as claimed in claim 2, wherein each of thesecond connecting portions each having the V-shape form is connected tothe corresponding first mass portion at its apex and connected to thesecond mass portion at its base ends.
 5. The actuator as claimed inclaim 2, wherein each of the V-shape forms of the first elasticconnecting portions and the second elastic connecting portions has asymmetrical shape with respect to the central axis for rotation of thefirst mass portions and the second mass portion.